1. Field of the Invention
This invention relates to electrodes for plasma etching apparatus using low temperature plasma technique and plasma etching apparatus using the same.
2. Description of the Related Prior Art
A conventional plasma etching apparatus is described with reference to the drawings, wherein FIG. 4(a) is a cross sectional structure view of the conventional plasma etching apparatus and FIG. 4(b) is an enlarged view of a circle 1 in FIG. 4(a). The atmosphere in an etching chamber 2 is discharged via an air outlet 3 into vacuum state. A bottom electrode platform 4 is made of insulating material. A bottom electrode 5 is mounted on the bottom electrode platform 3, which electrode holds thereon a substrate 6 to be etched. A top electrode 7 is designed to introduce an etching gas via a gas inlet 10 and guide the gas into the etching chamber 2 via gas distribution openings 11. Further, the bottom electrode 5 is electrically connected at a high frequency power supply node 8 to a high frequency power supply 9 and then grounded at 12. Plasm is generated between the etching chamber 2 and the top electrode 7. The bottom electrode 5 is cooled with a refrigerant 15 flowing from a refrigerant inlet 13 to a refrigerant outlet 14. The etching chamber 2 is also grounded at 16. As FIG. 4(b) indicates, the surface roughness of a surface of the bottom electrode 5 in the conventional apparatus is approximately 10 .mu.m or more.
FIGS. 4(a) and 4(b) illustrates mere placement of the substrate on the bottom electrode 5. Another method of mounting the substrate on the bottom electrode is a clamping technique by which the surface of the substrate is pressed down and He gas is introduced from rear.
Still another technique consists of disposing an insulating film on a surface of the bottom electrode 5 and applying a high DC voltage to the bottom electrode 5, by which an electric charge is injected into the insulating film and electrostatic absorption caused by the electric charge helps the bottom electrode 5 secure and hold the substrate to be etched.
Those conventional techniques are, however, not satisfactory in that the smoothness of the surface of the bottom electrode 5 is so poor as to deteriorate heat transfer to the substrate and increase the temperature of the surface of the substrate during etching process to thereby cause instable etching performance.
It is likely that the clamping technique would suffer from problems of dirty or damaged substrate, because the surface of the substrate is pressed down physically. A proposed solution to the problem is either to form an anti-erosion oxide film on an aluminum electrode as suggested in Japanese Laid-open Publication 63-658920 or to cover an electrode for plasm etching or plasma CVD with a coating of small sputtering efficiency.
The electrostatic absorption technique causes the substrate to be electrostatically absorbed upon application of the DC voltage to the bottom electrode 5. However, if plasma process takes place under the circumstance, then difficulty would be experienced in removing the substrate from the bottom electrode 5 while remaining absorbed. In case it is forcibly removed, the substrate would be scratched or damaged. For this reason, an anode oxide film is proposed in Japanese Laid-open Publication 2-240922 which is formed on an aluminum electrode with a metal in bores in the anode oxide film. The proposed anode oxide film prevents the substrate from being secured or attached to the bottom electrode 5 after plasma process.
Those conventional techniques might be able to minimize the generation of dust or the deterioration of the bottom electrode 5, individually. Those techniques are, however, unsuccessful in preventing reliability and stability of etching performances from becoming deteriorated due to temperature rise during etching process or preventing dust from generating during manual operation at the same time.
In particular, the clamping technique is unable to solve the problem that the substrate would become bent due to the pressure of helium (He) gas when the substrate of a large size is used.
For the electrostatic absorption technique, it is necessary to apply a very high DC voltage. Thus, the requirement for the insulating material forming the surface of the bottom electrode 5 is that breakdown voltage be high and leak current be small. Many of insulating materials currently in use in the semiconductor industry, however, are easy to be eroded once they are subjected to the etching atmosphere. The plasma etching apparatus is less reliable.
The present invention is to provide a plasma etching apparatus which is simple in construction, stable in etching performance and high in reliability.